FIRST: ALWAYS back up everthing on the card; it has to be formatted to upgrade the firmware.
Then get the latest firmware from the downloads section; it shouldn't be hard to find.
1.Insert the Writer into slot 2 and insert N-Card into slot 1.
2.Use USB cable connect to PC USB port directly. (Please do not use extension USB cable)
3.Hold "up+L+R+A+B" while starting your DS, now you should enter upgrade mode(a red colored text should appear).
(4. Extract the Firmware Archive.... It's more safe if you have it in a directory than trough a packer program)
5.Double click "NAND_ALL.bat" to run upgrade program. Please ignore if there some "found a badblock" appear when upgrade some 8G dslinker.
6.When it finished you will have to Quick Format your N-Card by holding DOWN+A+B+L+R when starting your DS.
7.After formating you have to copy "xmenu.dat" to the root (main directory, i.e. N:/ ) , If the xmenu.dat isn't on the card you won't be able to enter the Menu.
8.After the first time enter "GAME MODE", DSYSTEM folder will be set up. This folder you must not delete, or you will get an error when starting.

2) The latest Xmenu:

Go back to that same downloads area and download the xmenu.dat file. Take the xmenu.dat out of the downloaded file, and paste it over the old Xmenu, in the root of the card.